Can inductive loads help neutralize reactive loads?

[calipete]

Let me start by saying I know just enough on this subject to be dangerous.

I was wondering if an inductive load drawing a high current (VA) but little power (W), such as a high-efficiency motor running in vacuum, could help neutralize harmonic distortion caused by reactive loads, such as computer power supplies?

In practice, the idea is to connect a motor with no attached power consuming devices (Like pumps or fans) to the load side of transformers that are beginning to run hot due to high harmonic distortion levels. My assumption is that the back EMF of the electric motor could help offset current spikes in the wave forms of reactive loads, such as computer power supplies. Is this true?

The reason for considering this idea is that many small companies have problems with harmonic distortion in their computer rooms and with their supplying transformers. Most of these small companies don't have the funds to install expensive harmonic filters, larger transformers, or other costly solutions. Since motors are readily available at reasonable prices on the Internet, I figured this could be a cost effective solution, if it works.

Final note: I'm working to get my hands on an RPM power quality meter. Once I do, I will test this idea in a real-world environment and post my results here. In the meantime, I'd like to get theories from people who are more educated on the matter.

 

[waross]

Hi calipete
Actually induction is one form of reactance. Most loads are inductive. The inductive reaction is cancelled by capacitive reaction supplied by capacitors.
Harmonics are caused by non linear loads.
yours

 

[Skogsgurra]

I'm afraid you will need a real big motor to get any noticable improvement.

The reason is that harmonics always have a higher frequency than the fundamental. Three, five, seven etc are common multipliers.

That means that inductive reactance of a motor will also be three, five etc higher for the harmonics than for the fundamental. And since the transformer will have a much lower impedance than any motor you are likely to install, the net result is that the harmonics will continue to take the road of least impedance - i.e. going to the transformer secondary - as they always did.

It is only if you connect a motor with a very low impedance, compared to the transformer, that you will get any result. But that will be a very large motor and the excitation current it needs (even if run in vacuum or H2) will heat the transformer more than the harmonics.

Gunnar Englund

http://www.gke.org

 

[Skogsgurra]

Good afternoon waross. Are we alone in here tonight?

Gunnar Englund

http://www.gke.org

 

[waross]

Hi skogsgurra
Nice to see you back from your trip. Your absence was noticed.
I was thinking that if you doubled the base load by adding a non inductive load the harmonic component would appear less. Of course that would double the energy cost.
The corrolary to the increase in impedance of induction at higher frequency is the reduction in impedance of capacitors at higher frequencies.
Can you make some comments for the original poster? I'm not that strong on harmonics, but getting better.
respectfully

 

[ozmosis]

calipete
To determine how to solve a problem you first need to know what the problem is. You need to measure the harmonic distortion, understand where the problem is coming from and then decide a strategy to solve it. If the sites you are talking about are above limits of harmonic distortion then the nett effect of running a motor (that is not actually doing anything purposeful) will probably just add to the problem, as described by Gunnar.

 

[CJCPE]

Connecting an idle motor will only increase the current load on the power distribution system. Even if the power draw (W) is very small, the added reactive VA still means an increased current draw. The idle motor will not supply any harmonic current to the load. Power factor correction capacitors can supply harmonic current, but suitable capacitors would need to be selected and tuned for the application.